1. Field of the Invention
The invention relates to homogeneously doped Si crystals and somewhat more particularly to a method of restoring Si crystal lattice order after neutron irradiation.
2. Prior Art
Homogeneously doped Si crystals may be produced via neutron irradiation so that the nuclear reaction: ##STR1## occurs within the irradiated Si crystal. The silicon crystal utilized as the stock or starting material for the irradiation generally is produced by thermal decomposition of silicon-containing compounds and generally contains carbon as an impurity. This is known, for example, from N. Schink, "Determination Of Carbon In Trichlorosilane", Semiconductor Silicon, (The Electrochemical Society, 1969) pages 85-88. However, such neutron irradiation causes lattice disorder or damage detrimental to the electrical properties of the doped crystal. Such neutron-induced lattice damage may be removed by annealing. For example, German Letters Patent No. 1,214,789 suggests a method of producing homogeneously n-doped Si crystals by irradiating such crystals with thermal neutrons and then heat-treating the so-irradiated crystals at an elevated temperature for a sufficient period of time to remove the lattice damage cause by the neutron irradiation. In accordance with the prior art, the time period of the heat treatment is dependent upon the intensity of the neutron flux in the nuclear reactor during the irradiation process. Accordingly, the respective temperature and time is determined by the degree of crystal lattice damage or distortion produced by the irradiation process. The above-referenced prior art patent suggests that neutron-induced crystal lattice damage may be removed by annealing an irradiated Si crystal for 24 hours in a furnace at 1000.degree. C. Other prior art, for example, German Offenlegungsschrift No. 25 16 514 (owned by the instant assignee and substantially corresponding to Burtscher et al U.S. Ser. No. 676,646, filed Apr. 14, 1976, now abandoned) suggests that such annealing be carried out for a time period at least equal to the time period of a subsequent diffusion process and at a temperature at least as high as that utilized during such subsequent diffusion process.
However, it has been determined that when semiconductor components are produced from such prior art annealed crystals, the electrical properties, particularly the specific electrical resistance, sometimes vary during subsequent diffusion and the like processes.